A distinction exists between modes of operation for electric door openers (referred to generally in the art as “electric strikes”), namely, fail-safe or fail-secure.
In fail-safe mode, the strike is unlocked at any time that an actuator, such as a solenoid or motor, is de-energized, thus permitting exit through the door in event of a power failure.
In fail-secure mode, the strike is locked at any time that the actuator is de-energized, thus securing the door against opening in event of a power failure.
In the older prior art, the two modes of operation have generally required two different basic constructions, resulting in increased costs for manufacture and stocking of the different constructions. Thus, it has been desirable in the art to develop strike mechanisms wherein a basic arrangement may be positioned in either fail-safe or fail-secure mode simply by reconfiguring certain internal strike elements. Unfortunately, such prior art reconfiguring typically requires significant movement of various operating elements, often further requiring the removal of the door strike assembly itself. Thus, the process can be cumbersome, difficult to complete reliably, and/or time-consuming to carry out. Further, at least one prior art device provides a means for changing the positions of internal elements from outside the housing. The ready-accessibility of the means can be undesirable for maintaining securing in a fail-secure mode.
U.S. Pat. No. 5,788,295, entitled “Electric Door Opener with Multiple Position Armature Permitting Different Operation Modes”, discloses an electric door opener with a transmission lever (“trimmer” 6) pivotable about an axis 16 at a first end to lock and unlock a door latch 4. The transmission lever is actuable by a release lever (“armature” 8) pivotable about an axis 9 at a first end and having a shaped opening for receiving a head 17 of the transmission lever. A solenoid 13 includes a plunger 22 operable at the opposite end of the release lever. The release lever is adjustable by position to release or lock head 17 of the transmission lever. A rotation stop 10 is provided to switch the system between fail safe and fail secure modes by variably positioning the head 17 with respect to the opening.
The disclosed apparatus has at least two serious shortcomings.
First, the rotation stop to change fail-safe to fail-secure and vice versa, provided in the form of a turnable plug, can be readily tampered with using a simple tool.
Second, the contact point of the plunger to the release lever is at the distal end of the release lever from pivot axis 9, which requires a maximum stroke range of the solenoid plunger over which the internal air gap between the armature of the plunger and the core of the coil, and thus the pulling or holding force of the solenoid, necessarily varies substantially. Thus over some portion of the required range, the force of the solenoid available to hold the latch locked is relatively weak. Further, in a case where the actuating force is provided by a motor and the contact point of the motor's plunger or linkage is at the distal end of the release lever, the operating stroke of the motor needed to move the lever through its full range is maximized. What is needed is an arrangement wherein the required overall stroke of the actuating solenoid is shortened, thereby minimizing variation in air gap and solenoid strength. In the case of a motor actuated mechanism, what is needed is an arrangement wherein the operating stroke of the motor is minimized.
U.S. Pat. No. 6,390,520 B1, entitled “Door Opener”, the relevant disclosure of which is herein incorporated by reference, discloses an electric door opening mechanism which is operable in either a fail safe or fail secure mode according to whether electric power is connected or disconnected to a pair of coils acting upon lever-shaped rotatable armatures external to the coil. The disclosure includes provisions for adjustment of internal stops to the rotatable armatures and provisions for changing coil positions relative to the armatures.
A shortcoming of this apparatus is that, when changing between fail-safe and fail-secure modes, to properly position the coil and to establish the correct range of rotational stroke of the armature, two elements must be repositioned in two separate operations. The coil must be repositioned relative to the rotational armature and the fixed stop must be removed, inverted, and re-installed.
In addition, through the normal operation and usage of a strike and latch mechanism, metal particles abraded from mating metal surfaces, such as from the latch bolt and strike, may collect inside the strike housing and may cause binding of close-fitting components within the housing. For example, a solenoid plunger's movement can become sluggish or stuck from metal debris entering between the plunger and solenoid body or a motor's movement may become sluggish or stuck if debris enters the motor mechanism.
None of the known prior art discloses the improved device which remedies these shortcomings set forth herein.
What is needed in the art is an electric door strike wherein the mechanism may be changed easily between fail-safe and fail-secure modes; wherein the means for changing is not accessible without at least removal of an outer cover plate; wherein no repositioning of an actuator, such as a coil, solenoid or motor, is required to change between operating modes, and wherein binding of closed fitting moving components within the housing, such as a solenoid plunger or motor mechanism, is reduced.
It is a principal object of the present invention to simplify, without compromising security, the switching of an electric strike between fail-safe mode and fail-secure mode.